Ferric pickling of silicon steel

Abstract

The pickling process designed for pickling electrical steel strip in a continuous fashion comprising immersing the strip in at least one pickling tub. The pickling tub contains a mixture of HCl, Fe 2+ , and Fe 3+ and a low concentration of HF. Upon exiting the final pickling tub, the strip may be brushed or scrubbed to loosen any residual scale to form a clean strip.

What is claimed is: 
     
       1. A process for pickling silicon-containing electrical steel comprising treating the silicon-containing electrical steel with a mixture comprising HCl, HF, Fe 3+ , and Fe 2+ , wherein the concentration of HF is less than 3 weight %; and wherein the concentration of Fe 3+  is not less than about 2 weight %. 
     
     
       2. The process of  claim 1 , where the concentration of the Fe 3+  is from about 2 weight % to about 8 weight %. 
     
     
       3. The process of  claim 1 , where the concentration of HCl is from about 6 weight % to about 15 weight %. 
     
     
       4. The process of  claim 1 , where the concentration of HF is from 1 to 2 weight %. 
     
     
       5. The process of  claim 1 , where the concentration of HF is about 1.5 weight %. 
     
     
       6. The process of  claim 1 , where the concentration of Fe 2+  is less than about 6 weight %. 
     
     
       7. The process of  claim 1 , where hydrogen peroxide is not sprayed onto the steel. 
     
     
       8. The process of  claim 1 , where the steel is pickled in a continuous fashion. 
     
     
       9. The process of  claim 1 , where the temperature of the mixture is not less than about 140° F. 
     
     
       10. The process of  claim 1 , where the temperature of the mixture is not less than about 150° F. 
     
     
       11. The process of  claim 1 , where the silicon-containing electrical steel comprises less than 2 weight % silicon. 
     
     
       12. The process of  claim 1 , where the silicon-containing electrical steel comprises about 3 weight % silicon. 
     
     
       13. A pickling process for silicon-containing electrical steel comprising the steps of:
 placing the silicon-containing electrical steel in a pickling tub kept at a temperature ranging from about 165° F. to about 180° F. containing a mixture comprising Fe 3+ , HF, and HCl; where the tub is agitated, the mixture is continuously or periodically fed with an oxidant, HF, and HCl.